Pneumatic tire

ABSTRACT

A pneumatic tire capable of reducing rolling resistance and discharging static electricity generated during running, wherein each of a tread rubber, a breaker rubber, and a sidewall, respectively, has a volume specific resistivity of 1×10 8  Ω·cm or more, the pneumatic tire further including a conduction rubber embedded in the tread part so as to be at least partially exposed to a surface of the tread part, a coating rubber disposed on the upper part of the breaker part, a bead part rubber, and side part electroconductive rubber electrically connecting the conduction rubber to the beat part rubber, wherein each of the conduction rubber, the bead part rubber, the coating rubber and the side part electroconductive rubber has a volume specific resistivity of less than 10 8  Ω·cm.

This application is a continuation of application Ser. No. 13/693,611,filed Dec. 4, 2012. Application Ser. No. 13/693,611 is a divisional ofapplication Ser. No. 12/155,295, filed Jun. 2, 2008. Application Ser.No. 12/155,295 claims priority to: Japanese Patent Application No.2007-159029 filed Jun. 15, 2007; Japanese Patent Application No2007-172695, filed Jun. 29, 2007; Japanese Patent Application No.2007-188542, filed Jul. 19, 2007; and Japanese Patent Application No.2007-188547, filed Jul. 19, 2007. The entire contents of all of theforegoing applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a pneumatic tire improved in safety bykeeping low rolling resistance and reducing static electricity generatedduring tire running.

DESCRIPTION OF THE BACKGROUND ART

In recent years, various methods for using silica for a tread part, abreaker, a sidewall part, or the like of a tire have been proposed forthe purpose of reduction in tire rolling resistance as well as ofmaintenance of wet grip performance. However, a problem of lack insafety is raised in the case where silica is contained in a large amountsince electrical resistance of the tire is increased to generate sparkdue to static electricity, for example, during supply of fuel for avehicle, so that the fuel catches fire. Therefore, there is a demand fora tire that realizes of a reduction in rolling resistance andmaintenance of wet grip performance and is capable of preventing staticelectricity from being generated.

Japanese Patent Laying-Open No. 08-230407 discloses, as a pneumatic tirecapable of improving electroconductivity and preventing dischargephenomenon caused by accumulation of static electricity in a vehiclebody, a tire wherein: a rubber composition forming a tread part containscarbon black in a blending amount of 50 parts by weight or less withrespect to 100 parts by weight of a rubber component and a non-carbonblack in a blending amount of 40 parts by weight or less with respect to100 parts by weight of a rubber component; and an electroconductive thinfilm is disposed on the tread part and the sidewall part. It isdisclosed in the publication that a rubber component forming theelectroconductive thin film contains carbon black in a blending amountof 60 parts by weight or more with respect to 100 parts by weight of arubber component and in a ratio of 35 wt % of the whole rubbercomposition.

Japanese Patent Laying-Open No. 2000-190709 proposes a pneumatic tirecapable of maintaining excellent wet grip performance and effectivelyreducing tire electrical resistance as well as of stably exhibiting suchcharacteristics from an initial use to a wear limit of the tire. Thepublication proposes a pneumatic tire, wherein a tread rubber includes amain tread rubber part that is made from an insulating rubber materialhaving a volume specific resistivity of 1×10⁸ Ω·cm or more and an outerelectroconductive part that is made from a shoulder partelectroconductive rubber material having a volume specific resistivityof less than 1×10⁸ Ω·cm, forms a contact area together with a main treadpart, and ends with a gap of 3% to 35% of a contact area margin in atire axially inner direction from an edge of the contact area, the outerelectroconductive part is in the form of a sheet having a thickness of0.01 to 1.0 mm, exposed to a treat outer surface including a groove walland a groove bottom of a lateral groove to be continuous in a tirecircumferential direction; a wing rubber, a sidewall rubber, and aclinch rubber are formed of the shoulder part electroconductive rubbermaterial; and the outer electroconductive part is continued to the wingrubber.

Japanese Patent Laying-Open No. 10-036559 proposes, as a tire sidewallrubber composition capable of rendering a tire having small rollingresistance, wear resistance, excellent wet performance, and smallelectrical resistance, a tire sidewall rubber composition obtainable bymixing and kneading 100 parts by weight of a specific diene-basedrubber, 5 to 50 parts by weight of carbon black having a DBP oilabsorption amount of 120 ml/100 g or less and a CTAB surface area of 130m²/g or less, 10 to 60 parts by weight of precipitated silica having aDBP oil absorption amount of 200 ml/100 g or more and a BET nitrogenadsorption specific surface area of 180 m²/g or less, and a silanecoupling agent in an amount capable of controlling a reactive factorwithin a specific range.

Japanese Patent Laying-Open No. 08-034204 proposes a tire treadincluding a strip that is made from a tire tread rubber compositionhaving a high resistivity by using silica as a reinforcing agent and hasa predetermined side width while extending in a length direction and anelectroconductive strip that spreads in the length direction in the sidewidth and made from a tire rubber composition having a volumeresistivity of 10⁸ Ω·cm or less and a low resistivity.

However, in view of the methods in Japanese Patent Laying-Open Nos.08-230407, 2000-190709, 10-036559, and 08-034204, there is a demand forimprovement in satisfactory and excellent valance between low rollingresistance and high safety.

SUMMARY OF THE INVENTION

The present invention keeps low rolling resistance and effectivelyprevents accumulation of static electricity generated in a tire contactarea or a region where a tire contacts a rim during tire running.

According to the present invention, there is provided a pneumatic tireincluding a tread part, a sidewall part, a bead part, a carcassextending from the tread part to the bead part through the sidewallpart, and a breaker part disposed at an outside of the carcass in a tireradial direction, wherein each of a tread rubber, a breaker rubber, anda sidewall rubber formed on the tread part, the breaker part, and thesidewall part, respectively, has a volume specific resistivity of 1×10⁸Ω·cm or more, the pneumatic tire further including a side partelectroconductive rubber extending from at least both edges of thebreaker part to the bead along the outside of the carcass, a coatingrubber having a region for contact with the side part electroconductiverubber and disposed so as to coat an upper part of the breaker, aconduction rubber contacting the coating rubber and embedded in thetread part so as to be partially exposed to a surface of a tread, and abead part rubber contacting a lower end of the side partelectroconductive rubber and disposed at a region contacting a rimflange of the bead part, wherein the side part electroconductive rubber,the coating rubber, and the conduction rubber contain carbon blackhaving a nitrogen adsorption specific surface area of 600 m²/g or morein an amount of 5 parts by mass or more with respect to 100 parts bymass of a rubber component and a silica having a nitrogen adsorptionspecific surface area of 70 m²/g or more and 250 m²/g or less withrespect to 100 parts by mass of the rubber component, and each of theside part electroconductive rubber, the coating rubber, and theconduction rubber each have a volume specific resistivity of less than1×10⁸ Ω·cm.

A ketjen black is suitably used as the carbon black. The bead partrubber preferably has a volume specific resistivity of less than 1×10⁸Ω·m. A thickness of the side part electroconductive rubber is preferablyadjusted to a range of 0.2 to 2 mm.

In the pneumatic tire according to the present invention, rubberblending having small rolling resistance is used for the tread part, thebreaker part, and the sidewall part. On the other hand, the pneumatictire has a structure in which the bead part rubber is connected to thecoating rubber disposed on the upper part of the breaker part with theside part electroconductive rubber interposed therebetween, and iselectrically connected to the conduction rubber embedded in the treadpart so as to contact a road surface. By employing such a structure, itis possible to reduce tire rolling resistance and to effectively reduceaccumulation of static electricity generated in a tire contact area or aregion where the tire contacts the rim during tire rubbing. Therefore,it is possible to provide the pneumatic tire that maintains a low fuelconsumption tire property and is improved in safety in use.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a right half of a sectional view of a pneumatic tireaccording to Embodiment 1 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Basic Structure>

One example of a structure of the pneumatic tire of the presentinvention is as in FIG. 1 in which the upper right half of the crosssection of the tire is shown. Tire 1 is provided with tread rubber 7forming a tread part, sidewall rubber 8 forming a pair of sidewall partsextending from both ends of tread rubber 7 in a tire radially inwarddirection, clinch rubber 3 forming a clinch part located at an inner endof the sidewall parts, and chafer rubber 2 forming chafer part locatedat an upper part of a rim. Carcass 10 is bridged over the beat parts onboth sides, and a breaker rubber forming a breaker part is disposed at atire radially outside of carcass 10.

Carcass 10 is formed of at least one carcass ply for aligning a carcasscord, and the carcass ply is folded back from an inner part to anoutside in a tire axial direction around bead core 13 and bead apex 11extending from an upper end of bead core 13 to a sidewall directionthrough from the tread part and the sidewall part and locked by alocking part. Breaker part 9 is formed of at least two breaker pliesthat are aligned breaker cords, and the breaker cords are overlappedwith orientations thereof being alternated so that the breaker cordsintersects with each other. In the pneumatic tire of the presentinvention, a coating rubber 5 is provided between the tread part and thebreaker part.

The embodiment of the present invention is characterized in that a sidepart electroconductive rubber 14 having a region for contacting coatingrubber 5, being adjacent to carcass 10, and extending from at least theboth ends of the breaker part to a position contacting clinch rubber 3is disposed. Conduction rubber 6 is disposed in tread rubber 7 so as tocontact coating rubber 5 and be partially exposed to the contact areaand has a structure in which conduction rubber 6 is electricallyconnected to coating rubber 5, side part electroconductive rubber 14,and clinch rubber 3.

By employing the above structure, it is possible to discharge staticelectricity generated in the bead part rubber located at the regioncontacting the rim or the contact region during tire rubbing to theoutside of the tire through the electroconductive rubber members.

<Tread Rubber, Breaker Rubber, and Sidewall Rubber>

Each volume specific resistivity of the tread rubber, the breakerrubber, and the sidewall rubber forming the tire is set to 1×10⁸ Ω·cm ormore. Though carbon black has heretofore been used as a rubberreinforcing agent, it is possible to reduce rolling resistance by usingsilica in place of the carbon black. Further, since the silica is not anoil-derived material, silica is preferably used from the view point ofenvironment problems as compared to the carbon that is the oil-derivedmaterial. However, in the case of using silica, the volume specificresistivity tends to be increased. In the present invention, a reductionin tire rolling resistance and the basic characteristics such as rubberprocessability are maintained by basically containing silica, and theproblem of high electrical resistance of a volume specific resistivityof 1×10⁸ Ω·cm or more of a rubber composition is improved.

In the pneumatic tire of the present invention, 50 mass % or more of theabove-described filler contained in each of the tread rubber, thebreaker rubber, and the sidewall rubber is preferably a silica. In thecase where 50 mass % or more of the filler is the silica, an effect ofreducing the tire rolling resistance is good. A ratio of the silica inthe filler is preferably 70 mass % or more, more preferably 90 mass % ormore. In the present invention, all of the filler may be the silica, butother fillers are used in combination for the purpose of adjustingelectroconductivity and mechanical strength of each of the tread rubber,the breaker rubber, and the sidewall rubber.

The silica may be contained in an amount of 5 parts by mass or more and100 parts by mass or less with respect to 100 parts by mass of a rubbercomponent in each of the tread rubber, the breaker rubber, and thesidewall rubber. In the case where the silica blending amount is 5 partsby mass or more with respect to 100 parts by mass of the rubbercomponent, it is to possible to reduce tire rolling resistance. In thecase where the silica compounding amount is 100 parts by mass or less,it is possible to favorably prevent a reduction in processability due toviscosity increase of an unvulcanized rubber composition and excessiveincrease in cost.

As the silica, it is possible to use those generally used rubbers, andexamples thereof include dry method white carbon, wet method whitecarbon, colloidal silica, and the like. Among others, the wet methodwhite carbon mainly containing hydrous silicic acid is preferable.

The nitrogen adsorption specific surface area of silica (BET method) ispreferably in the range of from 100 to 300 m²/g, more preferably 150 to250 m²/g. In the case where the nitrogen adsorption specific surfacearea is 100 m²/g or more, a satisfactory reinforcing effect is achievedto favorably improve wear resistance of the tire. On the other hand, inthe case where the nitrogen adsorption specific surface area is 300 m²/gor less, processability of the rubbers during production is good, andgood tire driving stability is ensured. The nitrogen adsorption specificsurface area is measured by the BET method in accordance with ASTMD3037-81.

<Coating Rubber>

Coating rubber 5 in the present invention is provided disposed so as tocontact side part electroconductive rubber 4 and conduction rubber 6 andmade from a rubber having a volume specific resistivity set to less than1×10⁸ Ω·cm. It is possible to achieve a desired degree of tireelectroconductivity improvement effect when the volume specificresistivity is less than 1×10⁸ Ω·cm. Also, the volume specificresistivity may be set in the same manner as in the side partelectroconductive rubber and is preferably 1×10⁷ Ω·cm or less, morepreferably 1×10⁶ Ω·cm or less and is preferably 1×10³ Ω·cm or more, morepreferably 1×10⁴ Ω·cm or more.

It is possible to achieve a desired degree of the tireelectroconductivity improvement effect when a thickness of coatingrubber 5 is 0.2 mm or more, and the tire rolling resistance is notdeteriorated by a large degree when the thickness is 3.0 mm or less. Thethickness of the side part electroconductive rubber is preferably 0.5 to2.0 mm, particularly preferably in the range of from 0.9 to 1.5 mm. Itis sufficient that coating rubber 5 has the part contacting with theside part electroconductive rubber and the conduction rubber, and it isalso possible to provide coating rubber 5 allover the portion betweenthe tread part and the breaker part or to partially provide to aposition at which the conduction rubber is disposed or to a rangeexceeding the position.

The part of the coating rubber contacting the side partelectroconductive rubber is preferably in the form of a strip extendingin a tire circumferential direction and having a width of 5 mm or more,more preferably 10 mm or more. By contacting the side partelectroconductive rubber and the coating rubber under theabove-described conditions, it is possible to achieve a satisfactorytire electroconductive effect. The contact of the side partelectroconductive rubber with the conduction rubber is preferably thecontact with the whole part of the conduction rubber in a tire widthdirection.

In the present invention, the coating rubber may preferably containcarbon black that is contained in the range of from 30 to 100 parts bymass with respect to 100 arts by mass of a rubber component. In the casewhere 30 parts by mass or more of carbon black is contained with respectto 100 parts by mass of the rubber component, electroconductivity ofthecoating rubber is increased. In the case where the blending amount ofcarbon black is 100 parts by mass or less with respect to 100 parts bymass of the rubber component, durability is improved.The blending amountof carbon black with respect to 100 parts by mass of the rubbercomponent is preferably 35 parts by mass or more, more preferably 40parts or more by mass and is preferably 80 parts by mass or less, morepreferably 70 parts by mass or less.

The nitrogen adsorption specific surface area of carbon black containedin the coating rubber is preferably 600 m²/g or more and 1,500 m²/g orless. Mechanical strength of the coating rubber is good when thenitrogen adsorption specific surface area is 600 m²/g or more. Thenitrogen adsorption specific surface area of 1,500 m²/g or less ispreferred from the view point of ensuring processability duringproduction. The nitrogen adsorption specific surface area may morepreferably be 650 m²/g or more and is preferably 1,300 m²/g or less,more preferably 1,000 m²/g or less. As carbon black, wood tar carbonblack that is not an oil-derived stock is suitably used.

Silica or the like, for example, may be contained as a filler in thecoating rubber in addition to carbon black, but, from the view point ofimparting good electroconductivity, carbon black may preferably occupy 8mass %, more preferably 15 mass % or more, further preferably 100 mass %or more of the fillers.

In the case where the coating rubber contains silica, the blendingamount of silica is 10 parts by mass or more and 55 parts by mass orless, for example, with respect to 100 parts by mass of the rubbercomponent. It is possible to reduce the tire rolling resistance when thesilica blending amount is 10 parts by mass or more with respect to 100parts by mass of the rubber component, and the rolling resistance isdeteriorated when the silica blending amount exceeds 55 parts by mass.

The nitrogen adsorption specific surface area of silica (BET method) ispreferably in the range of from 70 to 250 m²/g, more preferably 80 to240 m²/g. In the case where the nitrogen adsorption specific surfacearea is 70 m²/g or more, a satisfactory reinforcing effect is achievedto favorably improve wear resistance of the tire. In the case where thenitrogen adsorption specific surface area is less than 250 m²/g,processability of the rubbers during production is good, and good tiredriving stability is ensured. The nitrogen adsorption specific surfacearea is measured by the BET method in accordance with ASTM D3037-81.

<Side Part Electroconductive Rubber>

A Side part electroconductive rubber 14 in the present invention has astructure in which side part electroconductive rubber 14 is adjacent toan outside of carcass 10 and extends to the bead part from the both endsof the breaker part through the sidewall part, so that a lower end ofside part electroconductive rubber 14 is electrically connected toclinch rubber 3. The volume specific resistivity of the side partelectroconductive rubber is set to less than 1×10⁸ Ω·cm. When the volumespecific resistivity of side part electroconductive rubber 14 is lessthan 1×10⁸ Ω·cm, it is possible to achieve an effect of improving tireelectroconductivity. The volume specific resistivity of the ply rubberis preferably set to 1×10⁷ Ω·cm or less, more preferably 1×10⁶ Ω·cm orless. When a rubber composition containing an electroconductivecomponent in a large amount is used, it is possible to reduce electricalresistance, while the rim is easily subjected to rusting due topromotion of an electrochemical reaction in a region at which the tirecontacts the rim. In order to avoid the rusting, the volume specificresistivity of the side part electroconductive rubber is preferably setto 1×10³ Ω·cm or more, more preferably 1×10⁴ Ω·cm or more. The side partelectroconductive rubber is disposed adjacent to the outside of thecarcass, and a part thereof may be disposed between the carcass and thebreaker and may be formed continuously in the tire circumferentialdirection.

As the rubber blending of side part electroconductive rubber 14, theblending substantially the same as that of the coating rubber may beused, and, from the view point of reducing rubber detachment at bothends of the breaker, it is possible to use a composition wherein rubberhardness and the like are adjusted.

<Conduction Rubber>

In the present invention, the conduction rubber is embedded into thetread part, be partially exposed to a tire contact area, and anotherpart is coupled to the coating rubber to effectively discharge staticelectricity generated during running of the pneumatic tire to thecontact area. Though conduction rubber 6 shown in FIG. 1 is embedded ata position at a central part of tread part 7, it is possible to embed aplurality ofthe conduction rubbers. The width W of the conduction rubberin a tire width direction may be 0.2 to 10 mm, preferably 0.9 to 1.5 mm.

Conduction effect is small when the width is less than 0.2 mm, while thecontact region of the conduction rubber in the tread part is relativelyincreased when the width exceeds 10 mm to impair the contactcharacteristics. Though it is preferable to form the conduction rubberas a continuous layer in the tire circumferential direction, theconduction rubber may be formed discontinuously in the tirecircumferential direction.

The volume specific resistivity of the conduction rubber is set to avalue smaller than those of the tread rubber, the breaker rubber, andthe sidewall rubber. The volume specific resistivity of the conductionrubber is less than 1×10⁸ Ω·cm. In the case where the volume specificresistivity of the conduction rubber is less than 1×10⁸ Ω·m,electroconductivity of the tire is improved to achieve effect ofdischarging static electricity. The volume specific resistivity of theconduction rubber is preferably 1×10⁷ Ω·cm or less, more preferably1×10⁶ Ω·cm or less.

In the present invention, when the volume specific resistivity of thetread rubber, the breaker rubber, and the sidewall rubber are set to1×10⁸ Ω·cm or more, since the volume specific resistivity of the sidepart electroconductive rubber, the coating rubber and the conductionrubber coupled to the coating rubber are set to values lower than thoseof the tread rubber, the breaker rubber, and the sidewall rubbers whilemaintaining the tire performance such as rolling resistance anddurability, it is possible to effectively discharge the staticelectricity generated in the pneumatic tire through the electricalconnection passage by the coating rubber, the side partelectroconductive rubber, the conduction rubber, and the like.

It is possible to impart electroconductivity to the conduction rubber ofthe present invention by adding thereto carbon black or metal foil inthe same manner as in the coating rubber as well as to employ blendingdesign for imparting electroconductivity based on the blending of thetread rubber from the view point of improving the contactcharacteristics.

<Bead Part Rubber>

As used herein, the bead part rubber means the clinch rubber or thechafer rubber. Static electricity is generated in a driving mechanismduring running of the tire, and the static electricity is accumulated inthe car and also inside the tire through the rim and the bead partrubber. It is necessary to effectively discharge the static electricityto the contact area through the side part electroconductive rubber.

Referring to FIG. 1, it is desirable that the bead part rubber, namelythe clinch rubber or the chafer rubber, is electrically connected to theside part electroconductive rubber. In FIG. 1, the clinch rubber is arubber layer denoted by reference numeral 3, of which an outsidecontacts the rim flange in a tire bead part, while an inner partcontacts the folding edge of carcass 10.

In FIG. 1, the chafer rubber is so disposed on a bead part outer surfaceas to contact the flange part from a base part of the rim. As usedherein, chafer rubber 2 means a rubber forming a chafer. That is, chaferrubber 2 means a cord coating rubber in the case where the chafer is acord ply layer or means a rubber of a rubber chafer in the case wherethe chafer is a rubber chafer. Chafer rubber 2 in FIG. 1 is shown as theone including the above-described meanings.

The present invention includes at least one of the clinch rubber and thechafer rubber as the bead part rubber. The volume specific resistivityof the bead part rubber 10⁸ is less than 1×10⁸ Ω·cm. Goodelectroconductivity of the tire is achieved by maintaining the volumespecific resistivity of the bead part rubber to less than 1×10⁸ Ω·cm.The volume specific resistivity of the bead part rubber is preferablyless than 1×10⁷ Ω·cm, more preferably 1×10⁶ Ω·cm. Since the bead partrubber, i.e., the cling rubber and the chafer rubber, is required tohave abrasion resistance, rigidity, and hardness, it is possible toadjust electrical resistance by a blending method of impartingelectroconductivity by adding carbon black or metal foil in the samemanner as in the side part electroconductive rubber or the conductionrubber.

<Carcass>

Carcass 10 in the present invention is formed of at least one carcassply aligning a carcass cord. The carcass ply has a structure wherein thecarcass cords that are aligned in parallel to each other are embedded inthe rubber. Examples of a fiber material for forming the carcass cordinclude rayon, nylon, polyester, aramid, and the like, and these may beused alone or in combination of two or more. Among the above materials,it is preferable to use rayon since rayon is a natural stock material,and it is preferable to contain 90 mass % or more of rayon with respectto the fiber materials forming the carcass cord.

Though the volume specific resistivity of the ply rubber is notparticularly limited, the volume specific resistivity may be set in thesame manner a in the tread rubber, the breaker rubber, and the sidewallrubber. When the volume specific resistivity is less than 1×10⁸ Ω·cm, itis possible to improve tire electroconductivity to achieve staticelectricity discharge effect in cooperation with the adjacent side partelectroconductive rubber. In this case, the volume specific resistivityof the ply rubber may be set to 1×10⁷ Ω·cm or less, more preferably1×10⁶ Ω·cm or less.

In the present invention, when the volume specific resistivity of thebreaker rubber and the sidewall rubber are set to 1×10⁸ Ω·cm or more,since the volume specific resistivity of the coating rubber, the sidepart electroconductive rubber, and the conduction rubber are set to thevalue lower than those of the breaker rubber and the sidewall rubberwhile maintaining tire performance such as rolling resistance anddurability, it is possible to further improve tire electroconductivityof the tire in cooperation with the coating rubber, the sideelectroconductive rubber, the conduction rubber, and the like (thestatic electricity generated in the pneumatic tire).

Further, the side part electroconductive rubber is disposed so as toalso contact the bead part rubber. Since the bead part rubber having thelow volume specific resistivity and the side part electroconductiverubber and the like are contact with each other in addition to thestructure wherein the side part electroconductive rubber, the coatingrubber, and the conduction rubber are continuous, it is possible toremarkably improve static electricity discharge efficiency through therim.

<Blending Design of Rubber Component>

The coating rubber, the side part electroconductive rubber, theconduction rubber, the ply rubber the chafer rubber, the clinch rubber,the tread rubber, the breaker rubber, and the sidewall rubber is formedof the following rubber compositions, for example.

Preferred examples of the rubber component include a natural rubber(NR), an epoxidized natural rubber, a deproteined natural rubber, and adiene-based synthetic rubber. Examples of the diene-based syntheticrubber include a styrene-butadiene rubber (SBR), a polybutadiene rubber(BR), a polyisoprene rubber (IR), an ethylene-propylene-diene rubber(EPDM), a chloroprene rubber (CR), an acrylonitrile-butadiene rubber(NBR), a butyl rubber (DR), and the like, and a rubber componentcontaining one or more of the diene-based synthetic rubbers is suitablyused. The ethylene-propylene-diene rubber (EPDM) means a rubbercontaining ethylene-propylene rubber (EPM) and a third diene component.Examples of the third diene component include a non-conjugated dienehaving 5 to 20 carbon atoms, such as 1,4-pentadiene, 1,4-hexadiene,1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, and 1,4-octadiene, or acyclic diene such as 1,4-cyclohexadiene, cyclooctadiene,dicyclopentadiene, an alkenylnorbornene such as5-ethylidene-2-norbornene, 5-butylidene-2-norbornene,2-methallyl-5-norbornene, and 2-isopropenyl-5-norbornene, and the like.Particularly, dicyclopentadiene, 5-ethylidene-2-norbornene, and the likeare preferred.

As the rubber component used for the coating rubber, the side partelectroconductive rubber, the conduction rubber, the chafer rubber, andthe clinch rubber, the diene-based rubber is preferred, and, amongothers, the natural rubber (NR), the styrene-butadiene rubber (SBR), thepolybutadiene rubber (BR), the polyisoprene rubber (IR), and theepoxidized natural rubber (ENR), the deproteined natural rubber, and thelike are preferred.

To the above-described rubber components, it is possible to add thefollowing compounding agents that are generally used in tire rubbercompositions as required.

In the present invention, it is preferable to add silica to the treadrubber, the breaker rubber, and the sidewall rubber as described above.In the case of adding silica to the rubber composition, it is preferableto add a silane-based coupling agent, preferably a sulfur-containingsilane coupling agent, in an amount of 1 mass % or more and 20 mass % orless to a silica mass.

By adding 1 mass % or more of the silane coupling agent, tire abrasionresistance is improved to thereby achieve a reduction in rollingresistance.When the blending amount of the silane coupling agent is 20mass % or less, the risk for occurrence of scorching during steps formixing and kneading and extruding the rubber is reduced.

Examples of the sulfur-containing silane coupling agent include3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoil-tetrasulfide,trimethoxysilylpropyl-mercaptobenzothiazoletetrasulfide,triethoxysilylpropyl-methacylate-monosulfide,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoil-tetrasulfide,bis-[3-(triethoxysilyl)-propyl]tetrasulfide,3-mercaptopropyltrimethoxysilane, and the like. Other usable examples ofthe silane-based coupling agent include vinyltrichlorosilane,vinyltris(2-methoxyethoxy)silane, γ-glycidoxypropyltrimethoxysilane,γ-methacryloxypropyltrimethoxysilane,γ-(2-aminoethyl)aminopropyltrimethoxysilane,γ-chloropropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and thelike.

In the present invention, it is possible to use another coupling agentin accordance with the usage, such as an aluminate-based coupling agent,a titanium-based coupling agent, or the like alone or in combinationwith the silane-based coupling agent.

It is possible to use for the rubber component another filler such ascarbon black, clay, alumina, talc, calcium carbonate, magnesiumcarbonate, aluminum hydroxide, magnesium hydroxide, magnesium oxide,titanium oxide, and the like alone or in combination of two or more.

It is possible to add a vulcanizing agent, vulcanization accelerator, asoftening agent, a plasticizer, an anti-aging agent, a foaming agent, ananti-scorching agent, and the like in addition to the above-describedsubstances.

An organic peroxide or a sulfur-based vulcanizing agent may be used asthe vulcanizing agent. Examples of the organic peroxide include benzoylperoxide, dicumyl peroxide, di-t-butyl peroxide, t-butyl-cumyl peroxide,methylethylketone peroxide, cumene hydroperoxide,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,2,5-dimethyl-2,5-di(benzoylperoxy)hexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexine-3 or1,3-bis(t-butylperoxypropyl)benzene,di-t-butylperoxy-diisopropylbenzene, t-butylperoxybenzene,2,4-dichlorobenzoylperoxide,1,1-di-t-butylperoxy-3,3,5-trimethylcyloxane,n-butyl-4,4-di-t-butylperoxyvalelate, and the like. Among the aboveorganic peroxides, dicumyl peroxide, t-butylperoxybenzene, anddi-t-butylperoxy-diisopropylbenzene are preferred. As the sulfur-basedvulcanizing agent, sulfur, morpholinedisulfide, and the like may beused. Among the above sulfur-based vulcanizing agents, sulfur ispreferred.

As the vulcanization accelerator, it is possible to use those containingat least one of sulfenamide-based, thiazole-based, thiuram-based,thiourea-based, guanidine-based, dithiocarbamine-based,aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, andxantate-based vulcanization accelerators.

As the anti-aging agent, it is possible to select from amine-based,phenol-based, imidazole-based compounds, a carbamic acid metal salt, anda wax as required.

In the present invention, a softener may be used in combination in orderto further improve kneading processability. Examples of the softenerinclude a petroleum softener such as process oil, lubricant oil,paraffin, liquid paraffin, petroleum asphalt, and vaseline, a fattyoil-based softener such as caster oil, flaxseed oil, rapeseed oil, andcoconut oil, wax such as tall oil, beeswax, carnauba wax, and lanoline,fatty acid such as linoleic acid, palmitic acid, a stearic acid, andlauric acid, and the like.

Examples of the plasticizer include DMP (dimethyl phthalate), DEP(diethyl phthalate), DBP (dibutyl phthalate), DHP (diheptyl phthalate),DOP (dioctyl phthalate), DINP (diisononyl phthalate), DIDP (diisodecylphthalate), BBP (butylbenzyl phthalate), DLP (dilauryl phthalate), DCHP(dicyclohexyl phthalate), anhydrous hydrophthalate ester, DOZ(di-2-ethylhexyl azelate), DBS (dibutyl sebacate), DOS (dioctylsebacate), acetyltriethyl citrate, acetyltributyl citrate, DBM (dibutylmaleate), DOM (2-ethylhexyl maleate), DBF (dibutyl fumarate), and thelike.

As the anti-scorching agent for preventing or delaying scorching,organic acidsuch as anhydrous phthalic acid, salicylic acid, and benzoicacid, a nitroso compound such as N-nitrosodiphenylamine,N-cyclohexylthiophthalimide, and the like may be used.

EXAMPLES

Hereinafter, the present invention will be described in more detailsbased on examples, and the present invention is not limited to theexamples.

Examples 1 and 2 and Comparative Examples 1 and 2 <Side PartElectroconductive Rubber, Coating Rubber, and Conduction Rubber>

Ingredients other than sulfur and the vulcanizing agent of each ofblending ingredients shown in Table 1 were mixed and kneaded using anairtight bunbury mixer at 150° C. for 4 minutes, sulfur and thevulcanizing agent were added to be mixed and kneaded at 95° C. for 2minutes, followed by performing an extrusion step and a calendar step inaccordance with a conventional method to thereby prepare compositions ofside part electroconductive rubber, coating rubber, conduction rubberand clinch rubber A2 to H2.

<Preparation of Tread Rubber, Sidewall Rubber, Breaker Rubber, andClinch Rubber>

Ingredients other than sulfur and the vulcanizing agent of each ofblending ingredients shown in Table 2 to 5 were mixed and kneaded usingan airtight bunbury mixer at 140° C. for 4 minutes, sulfur and thevulcanizing agent were added to be mixed and kneaded at 95° C. for 2minutes, followed by performing an extrusion step and a calendar step inaccordance with a conventional method to thereby prepare thecompositions of tread rubber J2,sidewall rubber K2, breaker rubber L2,and clinch rubber I2.

TABLE 1 Coating Rubber/ Side Part Conduction Rubber ElectroconductiveRubber Blending A2 B2 C2 D2 E2 F2 G2 H2 Diene-Based Rubber NR (TSR20grade) 100 100 100 100 100 100 100 100 Carbon N330(product of MitsubishiChemical Corporation) 55 — — — 50 — — — Silica VN3 (product of DegussaCorporation) — 55 50 40 — 50 45 35 Carbon Printex XE2B (product ofDegussa Corporation) — — 5 15 — — 5 15 Processed Oil Diana Process PS32(product of Idemitsu Kosan 5 — — — 10 — — — Co., Ltd.) Soybean OilSoybean Refined Oil (product of Nissin Oillio — 5 5 5 — 10 10 10 Group,Ltd.) Wax Sunnoc Wax (product of Ouchi Shinko Chemical 2 2 2 2 — — — —Industrial Co., Ltd.) Anti-Aging Agent Santflex 13 (Product of Flexsys)2 2 2 2 4 4 4 4 Stearic Acid Kiri (product of NOF Corporation) 2 2 2 2 22 2 2 Zinc Flower Zinc Oxide No. 1 (product of Mitsui Mining & 5 5 5 5 55 5 5 Smelting Co., Ltd.) Coupling Agent Si75 (product of DegussaCorporation) — 5 4 3 — 5 4 3 Sulfur Crystex HSOT20 (Product of Flexsys)5 5 5 5 1.5 1.5 1.5 1.5 Vulcanization Nocceler (product of Ouchi ShinkoChemical 2 2 2 2 0.75 0.75 0.75 0.75 Accelerator Industrial Co., Ltd.)Volume Specific log₁₀R 4.8 10.5 7.8 5.8 5.0 11.1 7.1 5.3 ResistivityRatio of Materials Derived from Stocks other than Petroleum (%) 63 94 9287 63 95 92 87

In Table 1, a nitrogen adsorption specific surface area of the carbon(Printex XE2B) is 880 m²/g.

TABLE 2 Clinch Rubber Blending I2 Natural Rubber 20 SBR1500 80 N220 50Aromatic Oil 5 Wax 1.5 Anti-Aging Agent 1 Stearic Acid 1.5 Zinc Flower3.5 Sulfur 1.6 Accelerator 0.8 Volume specific resistivity (Ω · cm) 1 ×10⁶

TABLE 3 Tread Rubber Blending J2 Natural Rubber 100 Silica VN3 50 SilaneCoupling Agent 5 Wax 1 Anti-Aging Agent 2 Stearic Acid 1 Zinc Flower 3Sulfur 1.5 Accelerator 1 Volume specific resistivity (Ω · cm) 1 × 10¹¹

TABLE 4 Sidewall Rubber Blending K2 Natural Rubber 100 Silica VN3 45Silane Coupling Agent 4.5 Wax 1 Anti-Aging Agent 3 Stearic Acid 1 ZincFlower 3 Sulfur 2 Accelerator 1 Volume specific resistivity (Ω · cm) 1 ×10¹¹

TABLE 5 Breaker Rubber Blending L2 Natural Rubber 100 N330 — Silica VN355 Silane Coupling Agent 5.5 Anti-Aging Agent 2 Cobalt Stearate 2Stearic Acid 1 Zinc Flower 10 Insoluble Sulfur 5.5 Accelerator 0.9Volume specific resistivity (Ω · cm) 1 × 10¹¹

In Tables 2 to 5, details of the blending agents are as follows.

-   Note 1: natural rubber is TSR20 (trade name) made in Thailand.-   Note 2: SBR1500 is styrene-butadiene rubber manufactured by JSR    Corporation.-   Note 3: N220 is carbon black manufactured by Cabot Japan K.K.    (nitrogen adsorption specific surface area: 111 m²/g; DBP oil    absorption amount: 115 ml/100 g)-   Note 4: N330 is carbon black manufactured by Mitsubishi Chemical    Corporation (nitrogen adsorption specific surface area: 79 m²/g; DBP    oil absorption amount: 105 ml/100 g).-   Note 5: Silica VN3 is VN3 (trade name) manufactured by Degussa    Corporation (nitrogen adsorption specific surface area: 210 m²/g).-   Note 6: A silane coupling agent is Si69 (trade name) manufactured by    Degussa Corporation.-   Note 7: Aromatic oil is X140 (trade name) manufactured by Japan    Energy Corporation.-   Note 8: Wax is Sunnoc N (trade name) manufactured by Ouchi Shinko    Chemical Industrial Co., Ltd.-   Note 9: An anti-aging agent is Antigen6C manufactured by Sumitomo    Chemical Co., Ltd.-   Note 10: Stearic acid is Stearic Acid Tsubaki (trade name)    manufactured by NOF Corporation.-   Note 11: Zinc flower is zinc oxide manufactured by Mitsui Mining &    Smelting Co., Ltd.-   Note 12: Sulfur is Sulfur Powder (trade name) manufactured by    Karuizawa Seirensha K.K.-   Note 13: A vulcanizing agent 1 is Nocceler NS-P (trade name)    manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.-   Note 14: Insoluble sulfur is Myuclon OT20 (trade name) manufactured    by Shikoku Chemicals Corporation.

Pneumatic tires (Examples 1 and 2 and Comparative Examples 1 and 2) eachhaving the structure shown in FIG. 1 and the size of 195/65R15 wereproduced by using the rubber compositions shown in Tables 1 to 5 incombinations shown in Table 6 for a tread part, a sidewall part, abreaker, a clinch rubber, a chafer rubber, a side part electroconductiverubber, and a conduction rubber by an ordinary vulcanization moldingmethod. Basic structure of the sample tires are as follows. Carcass ply:

Cord angle: 90 degrees in tire circumferential direction.

Cord material: polyester (1500 denier, 1670 dtex/2) Breaker:

Cord angle: 24×24 degrees in tire circumferential direction.

Cord material: steel

The thickness of the coating rubber was 0.8 mm, the thickness of theside part electroconductive rubber was 1 mm, and the width of theconduction rubber was 1.5 mm and continuous in the tire circumferentialdirection.

<Evaluation of Tire Performance> Volume Specific Resistivity

Sample pieces each having a thickness of 2 mm and a size of 15 cm×15 cmby using the rubber compositions of Tables 1 to 5 were produced, andeach volume specific resistivity was measured by using an electricalresistance meter R8340A (product of ADVANTEST) under the conditions of avoltage of 500 V, a temperature of 25° C., and a moisture of 50%. Theresults are shown in Tables 1 to 5. The larger the value is, the higherthe volume specific resistivity of the rubber composition.

Rolling Resistance

The pneumatic tires produced as described above were mounted to regularrims, and then a regular inner pressure of 2.0 MPa was charged. Rollingresistance was measured by using a rolling resistance testermanufactured by STL at a speed of 80 km/h and a load of 4.7 kN. By usinga rolling resistance coefficient (RRC) obtained by dividing the detectedrolling resistance (RR) by the load, rolling resistance (RR) of each ofExamples 1 and 2 and Comparative Examples 1 and 2 was calculated by wayof the following expression:

-   Rolling resistance (RR)=(RRC of Comparative Example 1/RRC of each of    Examples 1 and 2 and Comparative Example 2)×100, with the rolling    resistance of the Comparative Example 1 being set to 100. The    smaller the value, the smaller the rolling resistance and better the    performance. The results are shown in Table 6.

Tire Electroconductivity

The pneumatic tires produced as described above were mounted to regularrims, and then a regular inner pressure of 2.0 MPa was charged. Each ofthe tread parts was brought into contact with an iron plate at a load of4.7 kN to measure an electrical resistance value between the tire rimpart and the iron plate at an applied voltage of 100 V. The results areshown in Table 6.

TABLE 6 Comparative Comparative Example 1 Example 2 Example 1 Example 2Coating Rubber C2 D2 A2 B2 Conduction Rubber C2 D2 A2 B2 Side PartElectro- G2 H2  E2  F2 conductive Rubber Clinch Rubber  I2  I2  I2  I2Tread Rubber  J2  J2  J2  J2 Sidewall Rubber K2 K2 K2 K2 Breaker RubberL2  L2  L2 L2 Tire Electro- 1 × 10⁷ 1 × 10⁶ 1 × 10⁷ 1 × 10¹¹conductivity Rolling Resistance 106 104 100 103

Referring to Table 6, Comparative Example 1 does not contain any silicaand electroconductive carbon black in the coating rubber, the conductionrubber, and the side electroconductive rubber. Comparative Example 2 isan example of not contain any carbon black in the coating rubber, theconduction rubber and the side electroconductive rubber.

Examples 1 and 2 achieved both of improvements in rolling resistance andtire electroconductivity since the electroconductive rubber compositionhaving the volume specific resistivity of less than 1×10⁸ Ω·cm was usedfor the coating rubber, the conduction rubber, and the side partelectroconductive rubber, and since the volume specific resistivity ofthe tread part, the breaker, and the sidewall part was set to 1×10⁸ Ω·cmor more, from which it is apparent that the pneumatic tires according tothe present invention are excellent in both of the rolling resistanceand electroconductivity.

The pneumatic tire of the present invention capable of suppressing therolling resistance and effectively discharging static electricitygenerated in tire during tire rubbing is suitably used for vehicles suchas cars, tracks, buses, and heavy machineries.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

What is claimed is:
 1. A pneumatic tire comprising a tread part, asidewall part, a bead part, a carcass extending from said tread part tosaid bead part through said sidewall part, and a breaker part disposedat an outside of said carcass in a tire radial direction, wherein eachof a tread rubber, a breaker rubber, and a sidewall rubber formed onsaid tread part, said breaker part, and said sidewall part,respectively, has a volume specific resistivity of 1×10⁸ Ω·cm or more,said pneumatic tire further comprising side part electroconductiverubber extending continuously in the tire circumferential direction fromat least both edges of said breaker part to the bead part along theoutside of said carcass wherein a part thereof is disposed between thecarcass and the edges of the breaker part, a coating rubber having aregion for contact with said side part electroconductive rubber anddisposed so as to coat an upper part of the breaker part, a conductionrubber contacting the coating rubber and embedded in said tread part soas to be partially exposed to a surface of a tread, and a bead partrubber contacting a lower end of said side part electroconductive rubberand disposed at a region contacting a rim flange of said bead part,wherein said conduction rubber is formed in the tire circumferentialdirection, and has a width from 0.2 to 10 mm in a tire width direction,said coating rubber has a thickness from 0.2 mm or more and 3.0 mm orless, and has a contact part in a circumferential direction with theside part electroconductive rubber in width of 5 mm or more, and saidside part electroconductive rubber, said coating rubber, and saidconduction rubber each have a volume specific resistivity of less than1×10⁸ Ω·cm, and one bead part is electrically connected with the otherbead part through said side part electroconductive rubber and saidcoating rubber.
 2. The pneumatic tire according to claim 1, wherein saidtire comprises carbon black and said carbon black is a ketjen black. 3.The pneumatic tire according to claim 1, wherein said bead part rubberhas a volume specific resistivity of less than 1×10⁸ Ω·cm.
 4. Thepneumatic tire according to claim 1, wherein said side partelectroconductive rubber has a thickness in a range of from 0.2 to 2 mm.5. The pneumatic tire according to claim 1, wherein said side partelectroconductive rubber, said coating rubber, and said conductionrubber contain carbon black having a nitrogen adsorption specificsurface area of 600 m²/g or more in an amount of 5 parts by mass or morewith respect to 100 parts by mass of a rubber component and a silicahaving a nitrogen adsorption specific surface area of 70 m²/g or moreand 250 m²/g or less in an amount of 10 to 55 parts by mass with respectto 100 parts by mass of a rubber component.